Indium halides

InF₃ is a white solid, m.p. 1170 °C. Its structure contains 6 coordinate indium.

InCl₃ is a white solid, m.p. 586 °C. It is obtained by oxidation of indium with chlorine.[1] It is isostructural with AlCl₃.

InBr₃ is a pale yellow solid, m.p. 435 °C. It is isostructural with AlCl₃. It is prepared by combining the elements.[2] InBr₃ finds some use in organic synthesis as a water tolerant Lewis acid.[3]

InI₃ is a yellow solid. It is obtained by evaporation of a solution of indium in HI.[4] Distinct yellow and a red forms are known. The red form undergoes a transition to the yellow at 57 °C. The structure of the red form has not been determined by X-ray crystallography, however spectroscopic evidence indicates that indium may be six coordinate.[5] The yellow form consists of In₂I₆ with 4 coordinate indium centres. It is used as an "iodide getter" in the Cativa process.

In₇Cl₉ is yellow solid stable up to 250 °C that is formulated In^I₆(In^IIICl₆)Cl₃[7]

In₇Br₉ has a similar structure to In₇Cl₉ and can be formulated as In^I₆(In^IIIBr₆)Br₃[8]

In₅Br₇ is a pale yellow solid. It is formulated In^I₃(In^II₂Br₆)Br. The In^II₂Br₆ anion has an eclipsed ethane like structure with a metal-metal bond length of 270 pm.[9]

In₂Cl₃ is colourless and is formulated In^I₃ In^IIICl₆[10] In contrast In₂Br₃ contains the In₂Br₆ anion as present in In₅Br₇, and is formulated In^I₂(In^II₂Br₆) with a structure similar to Ga₂Br₃.[11]

In₄Br₇ is near colourless with a pale greenish yellow tint. It is light sensitive (like TlCl and TlBr) decaying to InBr₂ and In metal. It is a mixed salt containing the InBr−4 and InBr3−6 anions balanced by In⁺ cations. It is formulated In^I₅(In^IIIBr₄)₂(In^IIIBr₆) The reasons for the distorted lattice have been ascribed to an antibonding combination between doubly filled, non-directional indium 5s orbitals and neighboring bromine 4p hybrid orbitals.[12]

In₅Cl₉ is formulated as In^I₃In^III₂Cl₉. The In₂Cl3−9 anion has two 6 coordinate indium atoms with 3 bridging chlorine atoms, face sharing bioctahedra, with a similar structure to Cr₂Cl2−9 and Tl₂Cl2−9.[13]

InBr₂ is a greenish white crystalline solid, which is formulated In^IIn^III Br₄. It has the same structure as GaCl₂. InBr₂ is soluble in aromatic solvents and some compounds containing η⁶-arene In(I) complexes have been identified. (See hapticity for an explanation of the bonding in such arene-metal ion complexes). With some ligands InBr₂ forms neutral complexes containing an indium-indium bond.[14]

InI₂ is a yellow solid that is formulated In^IIn^IIII₄.

InF only known as an unstable gaseous compound.

The room temperature form of InCl is yellow, with a cubic distorted NaCl structure. The red high temperature (>390 K) form has the ${\displaystyle {\ce {\beta-TlI}}}$ structure.[15]

InBr is a red crystalline solid, mp 285 °C. It has the same structure as ${\displaystyle {\ce {\beta-TlI}}}$, with an orthorhombic distorted rock salt structure. It can be prepared from indium metal and InBr₃.

InI is a deep red purple crystalline solid. It has the same structure as ${\displaystyle {\ce {\beta-TlI}}}$. It can be made by direct combination of its constituent elements at high temperature. Alternatively it can be prepared from InI₃ and indium metal in refluxing xylenes.[16] It is the most stable of the solid monohalides and is soluble in some organic solvents. Solutions of InI in a pyridine/m-xylene mixture are stable below 243 K.[15]

Salts of InCl−4, InBr−4 and InI−4 are known. The salt LiInF₄ has been prepared,[17][18] however it has an unusual layer structure with octahedrally coordinated indium center. Salts of InF₆³⁻, InCl3−6 and InBr3−6 [19] have all been made.

The InCl2−5 ion has been found to be square pyramidal in the salt (NEt4)₂InCl₅, with the same structure as (NEt₄)₂ TlCl₅, but is trigonal bipyramidal in tetraphenylphosphonium pentachloroindate acetonitrile solvate.[20]

The InBr2−5 ion has similarly been found square pyramidal, albeit distorted, in the Bis(4-chloropyridinium) salt [21] and trigonal bipyramidal [22] in Bi₃₇InBr₄₈.

The In₂X−7 ions contain a single bridging halogen atom. Whether the bridge is bent or linear cannot be determined from the spectra. The chloride and bromide have been detected using electrospray mass spectrometry. The In₂I−7 ion has been prepared in the salt CsIn₂I₇.[5]

The caesium salts of In₂Cl3−9 and In₂Br3−9 both contain binuclear anions with octahedrally coordinated Indium atoms.[13]

In^IX₂⁻ is produced when the In₂X₆²⁻ ion disproportionates. Salts containing the In^IX2−3 ions have been made and their vibrational spectra interpreted as showing that they have C_3v symmetry, trigonal pyramidal geometry, with structures similar to the isoelectronic SnX−3 ions.

Salts of the chloride, bromide and iodide ions (Bu₄N)₂In₂X₆ have been prepared. In non-aqueous solvents this ion disproportionates to give In^IX−2 and In^IIIX−4.